A backlight is often used as a light source for display devices, such as Liquid Crystal Display (“LCD”) devices, in which a display panel is illuminated to display an image. Many new display devices utilize some form of Dynamic Backlight Control (“DBLC”), in which the illumination level of the backlight is adjusted in accordance with the light requirements of the image to be displayed on the display panel. In Dynamic Backlight Control, the illumination level of the backlight is modified based on the image data for a frame. In generalized terms, for dark images, the illumination level of the backlight is lower, and for bright images, the backlight illumination level is higher. Then, the inverse of the backlight illumination level is applied to the display panel light filter control (e.g., the LCD shutter), to compensate for the varying level of illumination from the backlight. The resulting image is the same as the original, i.e., the image with the backlight fully illuminated. Dynamic Backlight Control allows the power consumption of the backlight to be reduced while maintaining the visual brightness and quality of the display.
Dynamic Backlight Control systems typically utilize global dimming, and as a result the illumination level of the entire backlight must satisfy the light requirement of all of the pixels that make up the image. This means that some regions of the display that only require low backlight illumination levels have an unnecessarily high illumination level. Recently, methods for local dimming of independent light elements within a backlight have been developed. In local dimming methods, the backlight has a number of independently controllable light elements used to illuminate the display. The illumination level of each light element can be individually adjusted in correspondence with dark and bright areas of the image to be displayed on the display panel. Thus, requirements for a high level of illumination in one area of an image do not require the entire backlight to have a high level of illumination, and power is conserved.
On the other hand, uniformity of backlight illumination across the entire display panel is considered a desirable quality for displays as it improves the quality of the image, and backlights strive to illuminate the display panel evenly. Thus, backlights are carefully designed to result in a uniform spread of light across the display panel. For instance, when light emitting diodes (“LEDs”) are used to make the backlight, they are often carefully chosen and arranged to prevent dark or bright spots, and special diffuser sheets are also used to further spread the light that passes through them.
An architecture for a display system that can locally dim the backlight and also provide a high quality image is required.